Intensity Mapping

In our discussion of earthquake intensity you learned that the intensity of an earthquake varies from one location to another. If information from a large number of locations is collected and plotted on a map, zones of different intensity can be drawn. Such a map would show the geographic pattern of intensity or damage zones for the earthquake. The map below is an intensity map for the 1971 San Fernando Valley, California earthquake. This earthquake had a magnitude of approximately 6.6.

This map was prepared by sending questionnaires to people in the San Fernando area, asking them where they were when the earthquake occurred and what they observed. The data collected was then plotted on a map and intensity zones were drawn. Note how the shape of the intensity zones appears similar to a "bulls eye" with the highest intensities in the center and decreasing intensity with distance. Such a map could be made for the Pymatuning Earthquake. (The intensity map is from the US Geological Survey's 1994 Earthquake Information Bulletin)